Polymers, particularly thermoplastics, are in theory recyclable, but are often not recycled because of the cost of collecting, sorting and purifying the recycled plastics. Therefore, most plastics and other polymers such as elastomers, are disposed of with other trash, such as in landfills, where they are very chemically stable, and degrade minimally. One way of reducing the amount of stable polymers in landfills and the like is to produce polymers which are degradable, as by hydrolysis, biodegradation, or like processes.
It is known that under the proper conditions, polylactide is biodegradable, and polymers containing this repeat unit have been considered desirable for this reason. However, most polylactide polymers are plastics, that is their glass transition temperature (Tg) is above room temperature, and they may be crystalline. Polymers which contain lactide repeat units but yet have elastomeric-like properties would also be desirable.
U.S. Pat. No. 5,210,108 describes foam made from a star shaped polymer containing lactide repeat units. The foams produced are rigid, not elastomeric.
D. W. Grijpma, et al., Makromol. Chem. Rapid Commun., vol. 14, p. 155-161 (1992) report the synthesis of star block copolymers having polylactide blocks and trimethylene carbonate or a mixture of trimethylene carbonate and another lactone block. These copolymers have polylactide Tg's of 50.degree.-55.degree. C.